Crystal engineering and structural diversity of 2-aminopyridinium hypodiphosphates obtained by crystallization and dehydration†
Abstract
Organic–inorganic salts and ionic co-crystals of hypodiphosphoric acid (H4P2O6) with 2-aminopyridine (2ap) have been synthesized and characterized by X-ray crystallography, thermogravimetry, elemental analysis and Fourier-transform infrared spectroscopy. (2apH)4(H3P2O6)2(H2P2O6)·2H2O (1), (2apH)2(H2P2O6)·2H2O (4), (2apH)2(H2P2O6)·(H4P2O6) (6) and (2apH)2(H2P2O6)·2(2ap) (7) were obtained in crystalline form in a typical solution-crystallization process. Compounds (2apH)4(H3P2O6)2(H2P2O6)·0.4H2O (2), (2apH)4(H3P2O6)2(H2P2O6)·0.1H2O (3) and (2apH)2(H2P2O6) (5) were formed during dehydration processes of (1) and (4), respectively, which took place as destructive transformations. Further annealing of compound (5) results in its partial decomposition into the anhydrous form of compound (3). Water removal is associated with a rearrangement of the crystal architecture and with the partial deformation of hypodiphosphate anions from the typical staggered conformation towards an eclipsed one.